Previously, a system has been developed for the selective exchange of information between a group of n stations, each of which includes emitting and receiving members, wherein a channel connects the various stations and means are provided for controlling the transfer of information between the emitting and receiving members. The control means is formed by a group of n station control modules each of which is connected between the connecting channel and respective stations; each of the modules being formed by a processing unit and an associated memory to process data at each of the stations. The resulting information processing system at each station processes the information which is exchanged between the members of the station and those of other stations. One particular system of this type is disclosed in the previously mentioned application.
The connecting channel described in the previously mentioned application is a standard means of interconnecting the modules. The channel is not controlled by one specific module, but is controlled by each module in turn. This method of connection between modules makes it possible to attain high speeds of data transfer; the use of bidirectional receivers connected to the connecting channel allows data to be transferred over long distances. In FIG. 2 of the previously mentioned application, information is transferred in the form of a message from an adapter circuit (designated as ABj) which is located at one station and enables the connecting channel to be connected to a module (MOj) at that station, to an adapter circuit ABj which is located at another station and which enables the connecting channel to be connected to module MOj at the another station. The messages transmitted and received by a station are controlled by software and logic means of a connection controller (Cj) at each station. The transfer of data can only be initiated by a station which has command of the connecting channel. Two kinds of transfers are possible:
1. The transfer of data from a command station of a slave station, and
2. The transfer of data from a slave station to a command station.
Two modes of transfer are permitted:
1. The normal mode, involving transferring data from one station to another station, and
2. The "shared" mode involving distributing the data from one station to all the other stations.
A station cannot refuse to hand over command of the connecting channel to another station. It is open to a station which has command to initiate the transfer of a message to or from another station or other stations. If no transfer is requested or if a transfer has been completed, the station which has command is obliged to yield command of the connecting channel to the next station.
The system described in the previously mentioned application meets the requirements mentioned above satisfactorily and is well suited to the transmission of data between remote stations. On the other hand, this solution becomes expensive when the stations are closely spaced. In the arrangement described in the previously mentioned application, adapter circuit ABj is duplicated as many times as there are stations situated close together. It is therefore an object of the present invention to provide an arrangement which employs only one adapter circuit ABj for enabling a connecting channel to communicate with all of the stations of a group of closely spaced stations, wherein the logic of the modules associated with each of the stations may remain the same and which does not alter the characteristics of inter-station dialogues.